1. Field of the Invention
The present invention relates to electron beam exposure and, more particularly, to a multi-electron beam exposure method and apparatus for drawing patterns using a plurality of electron beams to directly draw patterns on a wafer, or to expose a mask or reticle, and a device manufacturing method using the same.
2. Description of the Related Art
Electron beam exposure apparatuses include: a point beam type apparatus which uses a spot-like beam; a variable rectangular beam type apparatus which uses a beam variable in its size and having a rectangular section; and a stencil mask type apparatus which uses a stencil to form a beam having a desired sectional shape.
The point beam type electron beam exposure apparatus is exclusively used for research and development purposes because of low throughput. The variable rectangular beam type electron beam exposure apparatus has a throughput higher than that of the point beam type apparatus by one to two orders, though the problem of throughput is still serious in exposing a pattern in which fine patterns having a size of about 0.1 xcexcm are highly integrated. The stencil mask type electron beam exposure apparatus uses a stencil mask having a portion corresponding to a variable rectangular aperture in which a plurality of repeated pattern through holes are formed. The stencil mask type electron beam exposure apparatus can advantageously form repeated patterns by exposure. If a semiconductor circuit needs so many transfer patterns that they cannot be formed in one stencil mask, a plurality of stencil masks must be prepared and used one by one. The time for exchanging the masks is required, resulting in a large decrease in throughput.
An apparatus for solving this problem is a multi-electron beam exposure apparatus that irradiates a sample surface with a plurality of electron beams along designed coordinates, deflects the electron beams along the designed coordinates to scan the sample surface, and at the same time, independently turns on/off the electron beams in correspondence with the pattern to be drawn, thereby drawing a pattern. The multi-electron beam exposure apparatus can draw an arbitrary pattern without using any stencil mask, so the throughput can be increased.
FIG. 17 shows the schematic arrangement of a multi-electron beam exposure apparatus. Reference numerals 501a, 501b, and 501c denote electron guns capable of independently turning on/off electron beams; 502, a reduction electron optical system for reducing and projecting the plurality of electron beams from the electron guns 501a, 501b, and 501c on a wafer 503; and 504, a deflector for deflecting the electron beams reduced and projected on the wafer 503.
The electron beams from the electron guns 501a, 501b, and 501c are deflected by the same amount by the deflector 504. With reference to the beam reference position, the positions of the respective electron beams are sequentially settled on the wafer and the beams are deflected in an array having an array interval defined by the minimum deflection width of the deflector 504. The electron beams expose different element exposure areas in exposure patterns to be formed.
FIGS. 18, 19, and 20 show a state in which the electron beams from the electron guns 501a, 501b, and 501c expose the corresponding element exposure areas in exposure patters (P1, P2, P3) to be formed in accordance with the same array. While the positions of the respective beams are settled and shifted on the array at the same time in the order of (1, 1), (1, 2), . . . , (1, 16), (2, 1), (2, 2), . . . , (2, 16), (3, 1), each beam is turned on at a position where an exposure pattern (P1, P2, P3) to be formed is present to expose the corresponding element exposure area in the exposure pattern (P1, P2, P3) to be formed.
In the multi-electron beam exposure apparatus, however, since a plurality of electron beams are deflected by the same minimum deflection width to simultaneously draw patterns, a pattern having a fractional size, with which a given electron beam has a deflection width other than an integer multiple of the minimum deflection width, cannot be drawn. To draw this pattern, the minimum deflection width must be set to a minimum deflection width corresponding to the greatest common divisor of a fractional pattern and an integral pattern corresponding to the current minimum deflection width. In general, since the new minimum deflection width becomes smaller than the old minimum deflection width, the amount of data for drawing increases.
The above problem will be described in detail below with reference to FIGS. 17 to 20. If all the exposure patterns P1, P2, and P3 to be formed are based on the design rule of 100 nm, the minimum deflection width is set to 25 nm, and a 100-nm pattern is drawn by scanning each electron beam four times. If only the pattern P3 is based on the design rule of 180 nm, the minimum deflection width is set to the greatest common divisor, 20 nm, of 100 nm and 80 nm. Assume that the element exposure area to be exposed by each electron beam is 3.6xc3x973.6 (xcexcm2). In this case, if the minimum deflection amount is 25 nm, the number of times of settling the position of each electron beam in exposing the element exposure area is 20,736. If the minimum deflection width is 20 nm, this number is 32,400. That is, in the presence of a fractional pattern, the number of times of settling increases about 1.5 times, and the amount of data for drawing also increases about 1.5 times.
When only the pattern P3 is based on the design rule of 180 nm, in practice, a pattern having a line width of 180 nm may be approximately drawn by scanning an electron beam seven times without changing the minimum deflecting width from 25 nm. In this case, however, the drawing precision decreases.
The present invention has been made to solve the above problems in the prior art, and has as its object to provide a multi-electron beam exposure method and apparatus which can suppress a decrease in throughput even in the presence of a fractional pattern in drawing patterns. It is another object of the present invention to provide a device manufacturing method capable of manufacturing a device with a precision higher than that in the prior art by using the multi-electron beam exposure method and apparatus.
In order to achieve the above objects, according to a preferable aspect of the present invention, there is provided a multi-electron beam exposure method of simultaneously drawing in a plurality of areas of a surface to be exposed by using a plurality of electron beams, comprising classifying drawing patterns into a plurality of groups in accordance with design rules, and drawing while changing a minimum deflection width of each electron beam in units of groups.
Preferably, drawing is sequentially performed in the respective areas of the plurality of groups. In addition, the diameter of each electron beam or the settling time therefor is changed in accordance with switching of the minimum deflection width.
According to another preferable aspect of the present invention, there is provided a multi-electron beam exposure method of deflecting a plurality of electron beams onto a surface to be exposed of an object with a minimum deflection width as a unit on the basis of drawing data, independently controlling irradiation of each electron beam for each deflecting operation, and drawing a pattern in an element exposure area in units of electron beams, thereby drawing in a subfield consisting of the plurality of element exposure areas and sequentially drawing in a plurality of subfields, comprising the step of classifying pattern groups in the drawing data into a plurality of groups on the basis of design rules, and determining an optimal minimum deflection width for each group in drawing each pattern group, the first dividing step of dividing the drawing data in units of the subfields, the second dividing step of dividing a subfield having a plurality of pattern groups into subfields each having only one pattern group, and the step of, in exposing a subfield having only one pattern group, switching the minimum deflection width to an optimal minimum deflection width corresponding to the group, and deflecting the plurality of electron beams with the optimal minimum deflection width as a unit, thereby drawing a pattern.
Preferably, the second dividing step comprises the step of comparing a drawing time required when the subfield is divided into subfields each having only one pattern group and drawing is sequentially performed in the respective subfields with an optimal minimum deflection width corresponding to the group in each subfield as a unit, with a drawing time required when drawing is performed in the subfield before a dividing operation with an optimal minimum deflection width corresponding to a plurality of groups belonging to the subfield as a unit, thereby determining whether to divide the subfield into subfields each having only one pattern group. Further preferably, the optimal minimum deflection width corresponding to the plurality of groups is a greatest common divisor of minimum deflection widths of the respective groups.
The method preferably further comprises the step of switching the diameters of the plurality of electron beams in accordance with switching of the minimum deflection widths in exposing each subfield.
The method preferably further comprises the step of switching the settling times for the plurality of electron beams in accordance with switching of the minimum deflection widths in exposing each subfield.
According to still another preferable aspect of the present invention, there is provided a device manufacturing method comprising the manufacturing step including the step of drawing a pattern using the method described above.
According to still another preferable aspect of the present invention, there is provided a multi-electron beam exposure apparatus for classifying pattern groups to be drawn into a plurality of groups based on pattern sizes, and deflecting a plurality of electron beams with optimal minimum deflection widths for the respective groups in drawing the classified groups, thereby drawing the pattern groups on a surface to be exposed, comprising deflection means for deflecting the plurality of electron beams onto the surface to be exposed, irradiation control means for independently controlling irradiation of each electron beam in each deflection operation, and control means for causing the deflection means to deflect the plurality of electron beams onto a surface to be exposed with a minimum deflection width as a unit, and causing the irradiation control means to independently control irradiation of each electron beam in each deflecting operation and draw a pattern in an element exposure area for each electron beam so as to draw in a subfield consisting of the plurality of element exposure areas, and for, when drawing is to be sequentially performed in a plurality of subfields, causing the irradiation means to inhibit irradiation of some of the plurality of electron beams so as to divide a subfield having a plurality of pattern groups into subfields each having one pattern group and draw in each subfield, thereby drawing while switching to an optimal minimum deflection width corresponding to the group in each divided subfield.
Preferably, the control means switches diameters of the plurality of electron beams in accordance with switching of the minimum deflection width. In addition, the control means switches settling times for the plurality of electron beams settled by the deflection means in accordance with switching the minimum deflection width.
In order to achieve the above objects, according to still another preferable aspect of the present invention, a multi-electron beam exposure method of deflecting a plurality of electron beams onto a surface of an object to be exposed with a minimum deflection width as a unit on the basis of drawing data while continuously moving a stage on which an object to be exposed is mounted, independently controlling irradiation of each electron beam for each deflecting operation, drawing a pattern in an element exposure area in units of electron beams so as to draw in a subfield consisting of the plurality of element exposure areas and sequentially drawing in a plurality of subfields, sequentially drawing in a plurality of subfields aligned in a direction perpendicular to a continuously moving direction to draw in a main field consisting of the plurality of subfields, and sequentially drawing in a plurality of main fields aligned in the continuously moving direction, comprising the step of classifying pattern groups in the drawing data into a plurality of groups on the basis of design rules, and determining an optimal minimum deflection width for each group in drawing each pattern group, the first dividing step of dividing the drawing data in units of the subfields, the second dividing step of dividing a subfield having a plurality of pattern groups into subfields each having only one pattern group, the first determination step of, in exposing a subfield having only one pattern group, determining to switch the minimum deflection width to an optimal minimum deflection width corresponding to the group, and deflect the plurality of electron beams with the optimal minimum deflection width as a unit, thereby drawing, the step of calculating a drawing time for reach main field, and the second determination step of determining to set a moving speed of the stage to a moving speed that allows drawing in each main field within the drawing time calculated for each main field.
Preferably, the second dividing step comprises the step of comparing a drawing time required when the subfield is divided into subfields each having only one pattern group and drawing is sequentially performed in the respective subfields with an optimal minimum deflection width corresponding to the group in each subfield as a unit, with a drawing time required when drawing is performed in the subfield before a dividing operation with an optimal minimum deflection width corresponding to a plurality of groups belonging to the subfield as a unit, thereby determining whether to divide the subfield into subfields each having only one pattern group. Further preferably, the optimal minimum deflection width corresponding to the plurality of groups is a greatest common divisor of minimum deflection widths of the respective groups.
The method preferably further comprises the step of switching the diameters of the plurality of electron beams in accordance with switching of the minimum deflection widths in exposing each subfield.
The method preferably further comprises the step of switching the settling times for the plurality of electron beams in accordance with switching of the minimum deflection widths in exposing each subfield.
The second determination step preferably comprises the step of determining a moving speed of the stage in units of main fields. Further preferably, the second determination step comprises the step of re-determining a moving speed of one of main fields adjacent in the continuously moving direction for which a higher moving speed is determined to set the moving speed to be lower than the determined moving speed so as to make a difference between the determined moving speeds of the adjacent main fields stay not more than a predetermined value.
Preferably, the method further comprises the step of sequentially drawing in a plurality of main fields aligned in the continuously moving direction to draw in a frame consisting of the plurality of main fields, and sequentially drawing in a plurality of frames aligned in a direction perpendicular to the continuously moving direction, and the second determination step comprises the step of determining a moving speed of the stage in units of frames.
According to still another preferable aspect of the present invention, there is provided a device manufacturing method comprising the manufacturing step including the step of drawing a pattern using the method described above.
According to still another preferable aspect of the present invention, there is provided a multi-electron beam exposure apparatus for classifying pattern groups to be drawn into a plurality of groups based on pattern sizes, and deflecting a plurality of electron beams with optimal minimum deflection widths for the respective groups in drawing the classified groups, thereby drawing the pattern groups on an object surface to be exposed, comprising a stage which moves with the object to be exposed being mounted thereon, deflection means for deflecting the plurality of electron beams into the surface to be exposed, irradiation control means for independently controlling irradiation of each electron beam in each deflection operation, and control means for causing the deflection means to deflect the plurality of electron beams onto a surface to be exposed with a minimum deflection width as a unit while continuously moving the stage, causing the irradiation control means to independently control irradiation of each electron beam in each deflecting operation and draw a pattern in an element exposure area for each electron beam so as to draw in a subfield consisting of the plurality of element exposure areas, sequentially drawing in a plurality of subfields aligned in a direction perpendicular to a continuously moving direction to draw in a main field consisting of the plurality of subfields, and for, when drawing is to be sequentially performed in a plurality of main fields aligned in the continuously moving direction, causing the irradiation means to inhibit irradiation of some of the plurality of electron beams so as to divide a subfield having a plurality of pattern groups into subfields each having one pattern group and draw in each subfield, thereby drawing while switching to an optimal minimum deflection width corresponding to the group in each divided subfield, and controlling the moving speed of the stage, on the basis of an exposure time for each main field, to a moving speed that allows exposure on each main field within the exposure time therefor.
Preferably, the apparatus further comprises means for switching diameters of the plurality of electron beams, and the control means switches the diameters of the plurality of electron beams in accordance with switching of the minimum deflection width.
Preferably, the apparatus further comprises means for switching diameters of the plurality of electron beams, and the control means switches settling times for the plurality of electron beams in accordance with switching of the minimum deflection width.
The control means preferably switches the moving speed of the stage when the main field in which drawing is to be performed changes. Further preferably, when the moving speed of the stage is switched, the control means controls the moving speed of the stage to make a difference between the moving speeds stay not more than a predetermined value.
Preferably, the control means causes the deflection means to deflect a plurality of electron beams so as to sequentially draw in a plurality of main fields aligned in the continuously moving direction, thereby drawing in a main field consisting of the plurality of main fields, causes the stage to step the object to be exposed so as to sequentially draw in a plurality of frames aligned in a direction perpendicular to the continuously moving direction, and switches the moving speed of the stage when the frame in which a pattern is to be drawn changes.
Preferably, the deflection means comprises an electromagnetic deflector and an electrostatic deflector, and the control means uses the electrostatic deflector to deflect the plurality of electron beams in the element exposure area and uses the electromagnetic deflector to deflect the plurality of electron beams from a subfield to a next subfield.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.